Ultrasonic diagnosis allows to display in real time how the heart beats or the fetus moves, by simply bringing an ultrasonic probe into contact with the body surface. This technique is highly safe, and hence allows repetitive examination. Furthermore, this system is smaller in size than other diagnosis apparatuses such as X-ray, CT, and MRI apparatuses and can be moved to the bedside to be easily and conveniently used for examination. Ultrasonic diagnostic apparatuses used in this ultrasonic diagnosis vary in type depending on the functions which they have. Some compact apparatuses which have already been developed are small enough to be carried with one hand. Ultrasonic diagnosis is free from the influences of exposure using X-rays and the like, and hence can be used in obstetric treatment, treatment at home, and the like.
Recently, an ultrasonic diagnosis apparatus has been implemented, which can acquire three-dimensional image data in real time by three-dimensionally scanning an object with ultrasonic waves and can generate and display a three-dimensional image or an arbitrary slice image. In addition, recently, a technique called three-dimensional tracking has been developed. This technique includes, first of all, inputting the initial contours (in the initial time phase) of the endocardium/epicardium of the left ventricle with respect to a plurality of MPR slices (typically, “two or more slices passing through the central cardiac chamber axis”) of the heart, forming three-dimensional contours in the initial time phase from the input initial contours, sequentially tracking a local myocardial region by performing technical processing such as pattern matching for the three-dimensional contours, calculating wall motion information such as the motion vectors and strain of the cardiac muscle from the tracking result, and quantitatively evaluating the myocardial wall motion (see, for example, patent reference 1). In addition, as a technique of displaying the result obtained by three-dimensional tracking, a technique of evaluating a cardiac function for each predetermined segment such as an ASE segment has been desired and implemented. As diagnosis images to display a three-dimensional tracking result, an MPR image and a parametric image superposed on it are used from the viewpoint of recognition performance. Such images allow to observe an analysis result on a predetermined MPR slice.
When, however, the respective segments three-dimensionally arranged on MPR slices are to be displayed by the conventional technique, segment boundaries are complicated depending on the positions of the MPR slices. This makes it difficult to understand the positional relationship between the respective segments and the respective MPR slices. Assume that after initial MPR slices (typically a plane A, a plane B perpendicular to the plane A, and three planes C perpendicular to the planes A and B) are set on a 4-ch view and slices perpendicular to it by automatic MPR setting or manually, initial contours are set on the slices. In most cases, the apex point set for three-dimensional tracking processing does not exist on the initial MPR slices, and the three planes C do not match the segmentation levels of the segments.
This occurs for the following reason. Initial MPR slices are set by using images corresponding to a 4-ch view and slices perpendicular to the 4-ch view around the central left ventricle axis. In general, however, although the left ventricles have semi-ellipsoidal shapes, they are slightly bent in the longitudinal direction in most cases. For this reason, the definition of a central left ventricle axis in three-dimensional tracking processing does not strictly match the real central left ventricle axis. That is, it is not possible to uniquely define a 4-ch view, and the defined position is merely an approximate position.
When defining the initial contours of the endocardial and epicardial surfaces of the left ventricle for three-dimensional tracking on such an approximate 4-ch view and slices perpendicular to it, the conventional technique inputs the information of a base or cardiac apical position and extracts the contours of the endocardial surface by an ACT method or the like or obtains an endocardial surface by, for example, extracting a totally three-dimensional endocardial surface after tracing the endocardial surface on the initial slices. This makes it possible to obtain an epicardial surface by, for example, assuming a predetermined myocardial thickness with respect to an endocardial shape. In addition, the left ventricular myocardium is segmented into predetermined segments based on the obtained endocardial surface and the initial 4-ch view position. The central left ventricle axis can be defined as the center (area centroid or the like) of the endocardial contours (annulus region contours) of the cardiac base. The cardiac apical position can be defined as the remotest endocardial position from the center of the cardiac base. Assuming that a line connecting the cardiac apical position and the center of the cardiac base is defined as a central axis, it is possible to perform segmentation by segmenting the left ventricle at predetermined angular intervals around the central left ventricle axis with reference to the cardiac base position of the initial MPR slices.
However, the cardiac apical position in the three-dimensional endocardial surface formed in the above manner does not always exist at the initial MPR slice positions, but rather exists at a different position in most cases. This is because the initial 4-ch view MPR slice used for setting and defining initial contours and segmentation does not sometimes include the cardiac apical position in an extracted endocardial surface.
In addition, the surfaces C are set to make the initial surface C positions coincide with approximate apical, mid, and base positions when viewed from a slices perpendicular to the approximate 4-ch view described above. However, there is no guarantee that even the surfaces C set in this manner correctly match the segment positions after the above segmentation.
Furthermore, the heart undergoes shortening between an end-diastolic period and an end-systolic period. It is therefore difficult to optimize surface C positions in advance (before segmentation) so as to make them always coincide with the apical, mid, and base positions.